Isn’t it time to start answering “what is a (blank)” questions with cladograms?
Posted on March 1st, 2008 by blue collar scientistSo I’m enjoying a low-pressure Saturday afternoon, clicking the “StumbleUpon” button, and it takes me to the Dinosaur Facts site - specifically, the page about Eudimorphodon. On that page I notice the following text:
The Eudimorphodon was a flying dinosaur that lived in the late Triassic period.
Now, I’m not an expert on dinosaurs. What I know about dinosaurs and carry about in my head would not be too much trouble to write down. But it seemed to me that Eudimorphodon was not a dinosaur, but in fact was a pterosaur. The picture certainly looked like that of a pterosaur. And I hadn’t really heard of non-feathered flying dinosaurs anyway. And one last objection - a flying dinosaur in the late Triassic? Not impossible, I suppose, but I don’t recall hearing of such a thing.
A quick look at Wikipedia seemed to confirm that Eudimorphodon is a pterosaur.
Now if there’s one thing that motivates me, it is finding errors. Having found this one, I decided to read the rest of the page. I read to the end and then I look at (what in print media would be called) the sidebar, which is titled Did you know, and which contains this gem:
Eudimorphodon was a pterosaur, not a dinosaur.
Er, ok then. Contradictory information on the same page just bugs me, but that’s the web for you. At least this time they had the right answer.
But here’s the thing. I don’t actually know what a Pterosaur is. Yes, I know that it is a flying Mesozoic reptile - I just don’t find that to be very meaningful. So I did a little web searching, and I quickly realized that for me, “what is a pterosaur” is answered not by the mantra about flying reptiles, not by their morphology, but by their phylogeny. Their phylogeny is not yet super-well established, which makes drawing firm conclusions chancy, but nevertheless cladograms exist. Looking for one led me to this image (from here):
So Pterosaurs are closer to the dinosaurs than crocodilians, but diverged before the dinosaurs originated. Nice. That’s actually a perfect answer - it tells me exactly why pterosaurs aren’t dinosaurs, and also suggests some attributes of Pterosaurs that it wouldn’t share with dinosaurs, or crocodiles.
So, why are we still using the mantra “flying reptile” to describe a Pterosaur? Phylogeny and phenotype together do a much better job, yes? Why do none of the benchmarks or standards used by the teachers I work with include cladograms? I’m sure this concept can and should be explained to 9-12 students.
Tags: ancestor, clade, cladeogram, dinosaur, evolution, phylogeny, pterosaur
March 1st, 2008 at 7:02 pm
The placement of pterosaurs among Archosauria is tenuous. Most studies find them as basal ornithodirs, somewhere between the Crurotarsi/Ornithodira split and Marasuchus. Others posit that they are merely basal archosaurs without a known ancestral branching point, while still other studies suggest a far more primitive origin–among the prolacertiformes or even lepidosauriformes.
There is no pterosaurian “Archaeopteryx,” which is very frustrating. We call them flying reptiles because that’s what they are–but so are birds, so it might be time to change the terminology!
March 3rd, 2008 at 12:46 pm
Those other studies don’t really show too much of anything, IMHO, or nothing useful anyway. (Peters’ analyses are also rather more noise than signal. Again, IMHO.) But anyway, I don’t believe the placement of pterosaurs within clade Archosauria can be considered tenuous without an appropriate line of positive evidence indicating such, and workers who wish to uproot the Pterosauria simply haven’t found one.
I’m not certain it’s necessary to alter the terminology every time our understanding of phylogenetic relationships changes, but I believe that is one of the reasons why lots of paleo workers now favor Sauropsida instead of Reptilia. But even so, I think it can be a useful means to educate students and/or the public about why birds (or whatever) are considered reptiles.
I don’t really know why cladograms haven’t made inroads into K-12 education. It actually sort of surprises me that they haven’t… I’ve explained their utility and use to my 8-year old nephew, so there is really no basis for excluding them.
(And it certainly would be nice to see Linnean taxonomies get left off all those otherwise decent wikipedia articles.)
March 3rd, 2008 at 3:07 pm
I wasn’t aware that Sauropsida was a replacement for Reptilia. I thought it was merely a higher taxon within Reptilia. Although that term has a lot of dogmatic baggage attached to it, I don’t see a good reason why Reptilia cannot operate in the same way that Synapsida does.
As for the Pterosauria, I think this is an area we will continue to disagree in until that memraneous Archaeopteryx is found. I agree that Peters is probably shouting at an empty room, but I will always favor more hypotheses than fewer. Actually, upon inspecting Big Boss the other day, I noticed an interesting point:
When Big Boss is sleeping, he often stretches his find limbs back toward his tail. But his feet face each-other, palm to palm. In this way, his first toes are along the substrate while the fifth toes, which are already divergent, point more or less toward each other. One can imagine a patagium forming along that divide. I’m not saying that lepidosaurs are the origin point. Rather, because that foot morphology seems to be broadly distributed across the Diapsida, I can just see it happening at virtually any level.
Well, if we only use pedal anatomy as the linkage.
March 4th, 2008 at 12:33 pm
“I wasn’t aware that Sauropsida was a replacement for Reptilia”
It probably isn’t (at least not formally). But that is my impression from my reading of much discussion.
“until that memraneous Archaeopteryx is found.”
Yes, I think something like this is what proponents of a non-Archosaurian Pterosauria need. It’s not that I disfavor lots of hypotheses (per se), but at some point, consensus tends to weed out poorly-supported hypotheses, which, at this point, does include non-Archosaurian Pterosauria.
That certainly doesn’t mean that it can’t be revisited in the future, once evidence is brought to the table. Shaking up the Archosauria would actually be rather exciting after all this time.
“Well, if we only use pedal anatomy as the linkage.”
Hah. Cladistics with one character. (Ahem. Sorry.)
March 19th, 2008 at 3:29 pm
You’re the first person besides myself involved in grade school education whom I’ve ever heard from who seems to understand this. I previously worked as an elementary school science lab specialist and used cladistics heavily. Certainly 4th, even 3rd graders can easily understand this when it is explained properly. “Classification” of living things has no meaning without cladistics in a post-Darwin world, as evolution is the foundation for all biological understanding. Otherwise, it is only ’stamp collecting’. This simple truth is not something that needs to be withheld until university-level biology courses. Thank you for trying to bring this to people’s attention.